Yes, there is more to that story. It will open up again later after a bunch of main story elements. Without wishing to give too much away, you will be asked to find someone and that person is important to continue the assassination storyline.

How much more of the story do I have to do? Would you say?

Quite a bit. After Skellige you’ll go to Kaer Morhen then back to Novigrad. Once in Novigrad again, Triss will have you find someone. Should be able to progress after that.

Damn so that’s like a whole 20 more hours

The three quests where you

1) Find Thaler

2) Try to find Philippa

3) Attack the Nilfgaardians with Roche and Ves

Must be done before going to the Isle of Mists. The quest where you actually assassinate Radovid isn't until you visit Novigrad later after fighting Imlerith. It'll be at some point after meeting Dijkstra in the bathhouse, as long as you didn't break his leg.

@Wagwan piffting23 are we talking about the Philippa mission where Radovid asks Geralt to find her? Or does the game give a second quest? And when does it trigger?

The Philippa mission where Radovid asks Geralt to find her. It triggers after you confront Whoreson Junior.

Okay so I did all three of those. Now just need to advance passed killing Imlerith